Bumpers of vehicles are designed to absorb energy and/or transfer energy during vehicle impacts. Such vehicle impacts may include frontal and rear impacts. Impacts may occur with objects of varying size and mass. For example, a vehicle may impact a relatively large, wide object such as another vehicle or a road barrier. Such impacts may be simulated with crash tests, such as a frontal impact test, a frontal oblique impact test, small offset rigid barrier (SORB) test, etc. Alternatively, the vehicle may impact narrower, lighter objects, such as pedestrians. These impacts may be simulated by pedestrian protection (PedPro) crash tests. Regardless of the size of the object being impacted, another consideration in the design of the bumper is low-speed damageability, which is simulated by crash tests that measure the amount of damage to the exterior of the bumper resulting from low-speed impacts. In these tests, little or no exterior damage to the bumper is desired to reduce the likelihood of costly repairs resulting from low-speed impacts.
These different classes of impacts present competing design factors for the bumper. During an impact with a larger, wider object, it may be more beneficial for the bumper to provide greater stiffness during deformation of the bumper to increase the energy absorbed. In contrast, during an impact with a narrower object that may be a pedestrian, it may be more beneficial to reduce the stiffness of the bumper during deformation, which may reduce injuries to the pedestrian. In further contrast, it may be beneficial for the bumper to be rigid, with no deformation, during low-speed damageability tests to reduce the likelihood of damage to the exterior of the bumper.